1. Field of the Invention
This invention relates to a vibration damping system for a vehicle, and more particularly to an improvement of a vibration damping system for a vehicle which has an actuator for vibrating a particular vibrating element such as the vehicle body, air in the cabin or the like and applies to the particular vibrating element vibration which is reverse to the vibration of the particular vibrating element in phase and equal to the vibration of the same in amplitude, thereby damping the vibration of the vehicle body or air in the cabin (noise).
2. Description of the Prior Art
As disclosed in Japanese Unexamined Patent Publication No. 1(1989)-501344, there has been known a vibration damping system for a vehicle in which vibration of a particular vibrating element on the vehicle body generated by vibration of the engine and the like is detected by a vibration sensor disposed in a predetermined position and an actuator for vibrating the particular vibrating element is controlled to apply vibration to the particular vibrating element to damp the vibration detected by the vibration sensor.
In various vibrations generated in a vehicle body, the vibration which is to be damped first varies depending on the condition of the vehicle such as the vehicle speed, the engine speed, whether the window is opened and the like. That is, where the vibration which is to be damped first is generated or the condition of the vibration, e.g., whether noise in the cabin increases or the vibration of the vehicle body increases, varies depending on the condition of the vehicle. Accordingly, in order to effectively damp various vibrations generated in the vehicle body, it is preferred that a number of vibration sensors be disposed in various positions on the vehicle body and each of the sensors be as sensitive as possible to be able to detect a fine change in vibration.
However even if a sensitivity of a certain vibration sensor is increased, if the vibration detected by the vibration sensor is not so related to the vibration to be damped, it will not be effective to control the actuator on the basis of the vibration signal output from the vibration sensor. Further when a plurality of vibration sensors are provided, the relations between the vibrations detected by the respective vibration sensors and the vibration to be damped will differ from vibration sensor to vibration sensor. That is, vibrations detected by some of the vibration sensors are deeply related to the vibration to be damped and vibrations detected by other vibration sensors are not. In the conventional vibration damping systems having a plurality of vibration sensors, the vibration signals output from the respective vibration sensors are all dealt with in the same way and the driving signal for controlling the actuator is always calculated on the basis of all the vibration signals. Accordingly, as the number of the vibration sensors increases, the amount of calculation to be performed in an unit time increases in vain and the vibration damping cannot be effected with a high efficiency.